Processes for calculating phased fetal genomic sequences

ABSTRACT

The present invention provides processes for calculating phased genomic sequences of the fetal genome using fetal DNA obtained from a maternal sample. The processes and systems of the present invention utilize novel technological and computational approaches to detect fetal genomic sequences and determine the phased heritable genomic sequences. The invention could be used, e.g., to identify in utero deleterious mutations carried by the parents and inherited by a fetus within a particular heritable genomic region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of provisional Patent ApplicationSer. No. 61/649,445, filed May 21, 2012 and is incorporated herein byreference.

FIELD OF THE INVENTION

The invention provides processes for calculating phased genomicinformation for a fetus using maternal samples including maternal blood,plasma and serum.

BACKGROUND OF THE INVENTION

In the following discussion certain articles and processes will bedescribed for background and introductory purposes. Nothing containedherein is to be construed as an “admission” of prior art. Applicantexpressly reserves the right to demonstrate, where appropriate, that thearticles and processes referenced herein do not constitute prior artunder the applicable statutory provisions.

An individual's genetic profile plays an important role in determiningrisk for disease and response to medical therapy. The development oftechnologies that facilitate rapid whole-genome sequencing will provideunprecedented power in the estimation of disease risk. Improvements insequencing technology have enabled cost effective generation of wholegenome sequences for individuals. By combining whole genome sequenceinformation with family or pedigree information or with longersequencing read technology, one may also now phase genomes. A phasedgenome will describe which variants are aggregated together withinchromosomal regions for a particular individual. The interrogation ofthe entire phased genome provides superior sensitivity to linked geneticfeatures and identification of recombination events.

It has been long recognized that certain sources of biological samplesfrom a pregnant mammal (e.g., blood or plasma), contains DNA from boththe mother and the fetus. This recognition has led to the use ofmaternal samples to identify, non-invasively to the fetus, fetal geneticcharacteristics, including qualitative (e.g., sex determination and RhDstatus) and quantitative (fetal copy number variations includingtrisomies) genetic detection of fetal sequences (for review see, e.g.,Lo et al., October 2011). It has also been demonstrated by deepsequencing of the cell-free DNA in a maternal sample that sequencesrepresentative of the entire fetal genome is present in circulation. (LoY-M et al., Sci Transl Med. 2010 Dec. 8; 2(61):61ra91.) However, thepercent fetal DNA is usually present in a low amount, usually 3-40%.Although deep, whole-genome sequencing of the fetal genome has beenperformed, with conventional technologies this approach is at presenteconomically infeasible for widespread clinical or commercial use.

Thus, improved processes and systems for the identification of inheritedalleles in a fetus from a maternal sample would be of great benefit inthe art. The present invention addresses this need.

SUMMARY OF THE INVENTION

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key or essentialfeatures of the claimed subject matter, nor is it intended to be used tolimit the scope of the claimed subject matter. Other features, details,utilities, and advantages of the claimed subject matter will be apparentfrom the following written Detailed Description including those aspectsillustrated in the accompanying drawings and defined in the appendedclaims.

The present invention provides processes for calculating phased genomicsequences of the fetal genome using fetal DNA obtained from a maternalsample. The processes and systems of the present invention utilize noveltechnological and computational approaches to detect fetal genomicsequences and determine the phased heritable genomic sequences. Theinvention could be used, e.g., to identify in utero deleteriousmutations carried by the parents and inherited by a fetus within aparticular heritable genomic region.

The processes of the invention provide methods for “phasing” the fetalDNA, i.e. determining the nucleic acids that are heritably linked withina single genomic region, e.g., a chromosome. The phased data from thefetal sequences can be used to determine whether the fetus is at riskfor many diseases, disorders and/or predispositions based on theinheritance of one or more heritable genomic regions present in thefetal genome.

In one aspect, the processes and systems of the invention utilizechromosome-specific genomic sequence information from the mother and/orfather, and preferably both the mother and father. In a preferredembodiment, the processes and systems utilize phased, whole-genome,chromosome-specific information of both the mother and father. Thissequence information from the mother and father may be obtained throughwhole genome sequencing or via other methods, e.g., array hybridizationfollowed by phasing of the sequence data from the mother and/or father.Such knowledge of the parental genomes can be used to determine whichclinically or phenotypically significant alleles are inherited in thefetus within a heritable genomic region.

In one aspect, the invention provides a computer-implemented process fordetermining the phased composition in a fetal heritable genomic region,comprising the steps of: providing phased sequence information from atleast one corresponding parental heritable genomic region; identifyingfive or more informative loci in the fetal DNA from a maternal samplecorresponding to a heritable genomic region of interest; determining thepaternal contribution of the heritable genomic region of interest basedon the identified paternal contribution of the five or more informativeloci; calculating the maternal contribution of the heritable genomicregion based on the determined paternal contribution and the five ormore informative loci; and predicting the likely phased composition ofthe phased fetal heritable genomic region based on the maternal andpaternal contributions of the heritable genomic region.

In another aspect, the invention provides a computer-implemented processfor determining the phased composition in a fetal heritable genomicregion, comprising the steps of: providing phased sequence informationfrom the maternal and paternal genome on at least one correspondingheritable genomic region; masking sequence information on loci that areindistinguishable between the maternal and paternal genome; providingempirical sequence information on five or more informative loci from amaternal sample corresponding to the heritable genomic region;calculating the predicted paternal contribution of the heritable genomicregion to the fetus based on the empirically identified paternalsequences of the five or more informative loci; calculating thepredicted maternal contribution of the heritable genomic region to thefetus based on the ratio of empirically identified sequences in thematernal sample; and providing a likelihood value of the fetal heritablegenomic region contributed by the maternal and/or paternal source basedon the predicted maternal and paternal contributions of the heritablegenomic region to the fetus.

In yet another aspect, the invention provides a computer-implementedprocess to calculate a value of likelihood for a fetal heritable genomicregion, comprising: providing maternal and paternal sequence informationfor a heritable genomic region; providing empirical sequence informationfrom a heritable genomic region within a maternal sample, wherein thesequence information is obtained from the maternal sample usingmassively parallel sequencing; identifying at least five informativeloci within the maternal and paternal heritable genomic region;calculating a value of the likelihood of the heritable genomic regioninherited by the fetus from the father based on the informative loci andthe empirical sequence information; identifying at least five loci whichare maternally and paternally heterozygous; and calculating a value ofthe likelihood of the heritable genomic region inherited by the fetusfrom the mother based on value of the likelihood of the heritablegenomic region inherited by the fetus from the father and the empiricalsequence information on the loci which are maternally and paternallyheterozygous.

In a preferred aspect of the invention, the fetal genetic variationwithin one or more heritable genomic regions can be imputed from asubset of parental informative loci within the heritable genomicregions. Thus, identifying certain alleles in the fetal genome can allowinformation of alleles that are not directly detected to be imputed fromthose that are detected. In this way, the heritable genomic regions inthe fetus can be identified from a subset of informative loci, andpreferably five or more informative loci, within thepaternally-inherited and maternally-inherited heritable genomic regions.

In some aspects the maternal sample is a cell free maternal sample, andpreferably maternal plasma or serum. In other aspects, the maternalsample comprises fetal cells.

In preferred aspects, the phased sequence information of parental genomeis provided by sequencing, and more preferably whole genome sequencing.Preferably this is accomplished using long-read sequencing technologiesthat are more effective in providing phased information, or by combiningshort-read with long-read sequencing technologies. When combiningsequencing technologies, the short-read coverage of the genome ispreferably 20× or greater and the long-read sequencing coverage of thegenome is preferably less than 5×. In other aspects, the phased allelicsequence information of the corresponding parental heritable genomicregion is determined in part by pedigree analysis.

Generally, the allelic sequence information from the fetus comprisessequence information from at least twenty informative loci in theheritable genomic region, although as few as five informative loci canbe used. In some aspects, the allelic sequence information from thefetus comprises sequence information on at least fifty informative lociin the heritable genomic region. In more specific aspects, the allelicsequence information from the fetus comprises sequence information on atleast one hundred informative loci in the heritable genomic region.

In certain aspects, phasing of the fetal nucleic acids is performed fora sub-chromosomal unit. In other aspects, phasing of the fetal nucleicacids is performed for an entire chromosome. In yet other aspects,phasing of the fetal nucleic acids is performed for multiple fetalchromosomes. In still other preferred aspects, it is performed for theentire fetal genome.

In some aspects, the fetal genomes are analyzed using sequencedetermination of fetal sequences, and assembly of heritable regions isperformed via comparison to one or more external reference sequences. Insome aspects, significant variants are grouped by chromosome andhaplotype association to determine which groups of variants areassociated in a heritable region.

It is a feature of the invention that the source of the fetal DNA can becell-free DNA obtained from maternal plasma or serum, and the processesof the invention identifies the fetal phasing in the background of thematernal DNA. The background maternal DNA contribution in the maternalsample can be “removed” from consideration either biochemically, throughsensitive detection and comparison of the frequency of haplotypespresent in the cell-free DNA, and/or via analytical analysis.

In some aspects of the invention, the processes utilize information onthe fetal contribution of both the maternal genome and the paternalgenome in the calculation of the phased fetal genomic regions.

In a preferred aspect, both maternal and paternal genomic information isused in the analysis of the fetal genome.

In other aspects, the association of significant variants in a fetalheritable region is determined by sequencing, and preferably massivelyparallel sequencing followed by allelic assembly.

DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram illustrating the difference between identificationof fetal alleles and phased allelic information.

FIG. 2 is a chart illustrating informative loci.

FIG. 3 is first illustration of fetal phased allelic chromosomes basedon the maternal and paternal genotyping.

FIG. 4 is a second illustration of fetal phased allelic chromosomesbased on the maternal and paternal genotyping.

FIG. 5 is a third illustration of fetal phased allelic chromosomes basedon the maternal and paternal genotyping.

FIG. 6 is a block diagram illustrating an exemplary system environment.

DETAILED DESCRIPTION OF THE INVENTION

The processes described herein may employ, unless otherwise indicated,conventional techniques and descriptions of molecular biology (includingrecombinant techniques), genomics, biochemistry, and sequencingtechnology, which are within the skill of those who practice in the art.Such conventional techniques include hybridization and ligation ofoligonucleotides, next generation sequencing, and detection ofhybridization using a label. Specific illustrations of suitabletechniques can be had by reference to the examples herein. However,equivalent conventional procedures can, of course, also be used. Suchconventional techniques and descriptions can be found in standardlaboratory manuals such as Green, et al., Eds., Genome Analysis: ALaboratory Manual Series (Vols. I-IV) (1999); Weiner, et al., Eds.,Genetic Variation: A Laboratory Manual (2007); Dieffenbach, Dveksler,Eds., PCR Primer: A Laboratory Manual (2003); Bowtell and Sambrook, DNAMicroarrays: A Molecular Cloning Manual (2003); Mount, Bioinformatics:Sequence and Genome Analysis (2004); Sambrook and Russell, CondensedProtocols from Molecular Cloning: A Laboratory Manual (2006); andSambrook and Russell, Molecular Cloning: A Laboratory Manual (2002) (allfrom Cold Spring Harbor Laboratory Press); Stryer, L., Biochemistry (4thEd.) W.H. Freeman, New York (1995); Gait, “Oligonucleotide Synthesis: APractical Approach” IRL Press, London (1984); Nelson and Cox, Lehninger,Principles of Biochemistry, 3^(rd) Ed., W.H. Freeman Pub., New York(2000); and Berg et al., Biochemistry, 5^(th) Ed., W.H. Freeman Pub.,New York (2002), all of which are herein incorporated by reference intheir entirety for all purposes. Before the present compositions,research tools and processes are described, it is to be understood thatthis invention is not limited to the specific processes, compositions,targets and uses described, as such may, of course, vary. It is also tobe understood that the terminology used herein is for the purpose ofdescribing particular aspects only and is not intended to limit thescope of the present invention, which will be limited only by appendedclaims.

It should be noted that as used herein and in the appended claims, thesingular forms “a,” “an,” and “the” include plural referents unless thecontext clearly dictates otherwise. Thus, for example, reference to “anucleic acid region” refers to one, more than one, or mixtures of suchregions, and reference to “an assay” includes reference to equivalentsteps and processes known to those skilled in the art, and so forth.

Where a range of values is provided, it is to be understood that eachintervening value between the upper and lower limit of that range—andany other stated or intervening value in that stated range—isencompassed within the invention. Where the stated range includes upperand lower limits, ranges excluding either of those included limits arealso included in the invention.

Unless expressly stated, the terms used herein are intended to have theplain and ordinary meaning as understood by those of ordinary skill inthe art. The following definitions are intended to aid the reader inunderstanding the present invention, but are not intended to vary orotherwise limit the meaning of such terms unless specifically indicated.All publications mentioned herein, and in particular patent applicationsand issued patents, are incorporated by reference for the purpose ofdescribing and disclosing various aspects, details and uses of theprocesses and systems that are described in the publication and whichmight be used in connection with the presently described invention.

In the following description, numerous specific details are set forth toprovide a more thorough understanding of the present invention. However,it will be apparent to one of skill in the art that the presentinvention may be practiced without one or more of these specificdetails. In other instances, features and procedures well known to thoseskilled in the art have not been described in order to avoid obscuringthe invention.

Definitions

The terms used herein are intended to have the plain and ordinarymeaning as understood by those of ordinary skill in the art. Thefollowing definitions are intended to aid the reader in understandingthe present invention, but are not intended to vary or otherwise limitthe meaning of such terms unless specifically indicated.

The term “amplified nucleic acid” is any nucleic acid molecule whoseamount has been increased at least two fold by any nucleic acidamplification or replication process performed in vitro as compared tothe starting amount in a maternal sample.

The term “diagnostic tool” as used herein refers to any composition orassay of the invention used in combination as, for example, in a systemin order to carry out a diagnostic test or assay on a patient sample.

The term “DNA contribution” refers to the percentage, proportion ormeasurement such as weight by volume of nucleic acid in a sample that iscontributed by a source, such as the mother or a fetus.

The term “extrinsic factor” includes any information pertinent to thecalculation of an odds ratio that is not empirically derived throughdetection of a maternal and fetal locus. Examples of such extrinsicfactors include information related to maternal age, information relatedto gestational age, information related to previous pregnancies with ananeuploid fetus, previous serum screening results, ultrasound findingsand the like. In preferred embodiments, the step of calculating and/oradjusting the computed odds ratio uses extrinsic factors related to bothmaternal age and gestational age.

The term “genetic feature” includes any feature within a genome that isidentifiable using, e.g., techniques such as sequence determination orhybridization. Genetic features include, but are not limited to, singlenucleotide polymorphisms, tandem single nucleotide polymorphisms, shorttandem repeats, expansions (e.g., triplet code repeats), methylationpatterns, and the like.

The term “heritable region” as used herein includes any larger portionof DNA from a single allele that can be elucidated using conventionalphasing technologies available to those in the art. In certain preferredaspects, the heritable region is a chromosome. In most preferredaspects, multiple heritable regions are detected, and most preferablythus includes a subset of the chromosomes from a parent, and in a morepreferred aspect all of the chromosomes inherited from a parent.

The term “hybridization” generally means the reaction by which thepairing of complementary strands of nucleic acid occurs. DNA is usuallydouble-stranded, and when the strands are separated they willre-hybridize under the appropriate conditions. Hybrids can form betweenDNA-DNA, DNA-RNA or RNA-RNA. They can form between a short strand and along strand containing a region complementary to the short one.Imperfect hybrids can also form, but the more imperfect they are, theless stable they will be (and the less likely to form).

The terms “locus” and “loci” as used herein refer to a nucleic acidregion of known location in a genome.

The term “informative locus” as used herein refers to a locus or pair ofloci with one or more distinguishing regions useful in determining thephasing of a fetal heritable region.

The term “maternal sample” as used herein refers to any sample takenfrom a pregnant mammal which comprises a maternal source and a fetalsource of nucleic acids (e.g., RNA or DNA).

The term “non-maternal” allele means an allele with a polymorphismand/or mutation that is found in a fetal allele (e.g., an allele with ade novo SNP or mutation) and/or a paternal allele, but which is notfound in the maternal allele.

The term “phasing” as used herein refers to determination of geneticfeatures which are located within a heritable region, e.g., the allelesthat reside in a particular genomic region of a chromosome. For example,phasing can be performed on an entire chromosome to determine whichgenetic features will be heritably linked. Phasing thus provides theability to distinguish which alleles belong to which chromosome, and toidentify which alleles will be inherited together upon meiosis.

As used herein “polymerase chain reaction” or “PCR” refers to atechnique for replicating a specific piece of target DNA in vitro, evenin the presence of excess non-specific DNA. Primers are added to thetarget DNA, where the primers initiate the copying of the target DNAusing nucleotides and, typically, Taq polymerase or the like. By cyclingthe temperature, the target DNA is repetitively denatured and copied. Asingle copy of the target DNA, even if mixed in with other, random DNA,can be amplified to obtain billions of replicates. The polymerase chainreaction can be used to detect and measure very small amounts of DNA andto create customized pieces of DNA. In some instances, linearamplification processes may be used as an alternative to PCR.

The term “polymorphism” as used herein refers to any geneticcharacteristic in a locus that may be indicative of that particularlocus, including but not limited to single nucleotide polymorphisms(SNPs), methylation differences, short tandem repeats (STRs), and thelike.

The term “polymorphic locus” as used herein refers to a locus with twoor more detectable alleles within a population. Generally, a polymorphiclocus will have the most common allele less than 70%.

Generally, a “primer” is an oligonucleotide used to, e.g., prime DNAextension, ligation and/or synthesis, such as in the synthesis step ofthe polymerase chain reaction or in the primer extension techniques usedin certain sequencing reactions. A primer may also be used inhybridization techniques as a means to provide complementarity of anucleic acid region to a capture oligonucleotide for detection of aspecific nucleic acid region.

The term “research tool” as used herein refers to any composition orassay of the invention used for scientific enquiry, academic orcommercial in nature, including the development of pharmaceutical and/orbiological therapeutics. The research tools of the invention are notintended to be therapeutic, to be diagnostic or to be subject toregulatory approval; rather, the research tools of the invention areintended to facilitate research and aid in such development activities,including any activities performed with the intention to produceinformation to support a regulatory submission.

The term “selected nucleic acid region” as used herein refers to anucleic acid region corresponding to a genomic region on an individualchromosome. Such selected nucleic acid regions may be directly isolatedand enriched from the sample for detection, e.g., based on hybridizationand/or other sequence-based techniques, or they may be amplified usingthe sample as a template prior to detection of the sequence. Nucleicacids regions for use in the processing systems of the present inventionmay be selected on the basis of DNA level variation between individuals,based upon specificity for a particular chromosome, based on CG contentand/or required amplification conditions of the selected nucleic acidregions, or other characteristics that will be apparent to one skilledin the art upon reading the present disclosure.

The terms “sequencing”, “sequence determination” and the like as usedherein refers generally to any and all biochemical processes that may beused to determine the order of nucleotide bases in a nucleic acid.

The term “specifically binds”, “specific binding” and the like as usedherein, refers to one or more molecules (e.g., a nucleic acid probe orprimer, antibody, etc.) that bind to another molecule, resulting in thegeneration of a statistically significant positive signal underdesignated assay conditions. Typically the interaction will subsequentlyresult in a detectable signal that is at least twice the standarddeviation of any signal generated as a result of undesired interactions(background).

The term “value of the likelihood” refers to any value achieved bydirectly calculating likelihood or any value that can be correlated toor otherwise indicative of a likelihood.

The term “value of the probability” refers to any value achieved bydirectly calculating probability or any value that can be correlated toor otherwise indicative of a probability.

THE INVENTION IN GENERAL

The present invention provides methods for identifying the particularalleles in a fetal genome using a subset of allelic information from thefetus using a maternal sample and a determination of the phased genomicdata of the mother and/or father. Phased data provides information notjust on the genotype of the parent (i.e., the two alleles that areinherited for a particular genomic region), but also the organization ofthe genetic information (e.g., the haplotypes that are linked on aparticular chromosome).

As a parent generally passes one of the two copies of each chromosome onto their offspring, the genes received by a child are typicallyheritably linked since they are located on the same chromosome.Knowledge of the phased genomic information of the parents allows asubset of alleles to be samples in the fetal genome to identify thelikelihood that a fetus has inherited a particular chromosome from themother and/or father.

The fetal genotypes are determined from a maternal sample, preferablycell-free DNA from a maternal blood sample. In one example, onedetermines the fetal genotype where the mother is homozygous and thefetus is heterozygous. In those instances, one identifies the “minor”allele. In another example, one determines the fetal genotype where themother is heterozygous and the fetus is homozygous. This may be done byfirst genotyping the mother from a pure cellular sample and thencomparing that genotype to that of the genotype from the maternal sampleto observe a shift in the expected counts.

In one example, the maternal sample is genotyped at more than 5,000locations in all chromosomes. In another example the sample is genotypedat more than 10,000 locations in all chromosomes. In another example,the sample is genotyped at more than 20,000 locations in allchromosomes. In another example, the sample is genotyped at more than50,000 locations in all chromosomes. In another example, the sample isgenotyped at more than 100,000 locations in all chromosomes.

The genotyping may be done with many different assays and detectionplatforms. With respect to preferred genotyping assays, one thatfacilitates high multiplexing is desirable.

In a preferred aspect, the maternal and fetal DNA is interrogated usingsequence determination of universally amplified sequences. In certainaspects, this utilizes one of the following combined selective anduniversal amplification techniques: (1) LDR coupled to PCR; (2) primaryPCR coupled to secondary PCR coupled to LDR; and (3) primary PCR coupledto secondary PCR. Each of these aspects of the invention has particularapplicability in detecting certain nucleic acid characteristics.However, each requires the use of coupled reactions for multiplexdetection of nucleic acid sequence differences where oligonucleotidesfrom an early phase of each process contain sequences which may be usedby oligonucleotides from a later phase of the process.

Barany et al., U.S. Pat. Nos. 6,852,487, 6,797,470, 6,576,453,6,534,293, 6,506,594, 6,312,892, 6,268,148, 6,054,564, 6,027,889,5,830,711, 5,494,810, describe the use of the ligase chain reaction(LCR) assay for the detection of specific sequences of nucleotides in avariety of nucleic acid samples.

Barany et al., U.S. Pat. Nos. 7,807,431, 7,455,965, 7,429,453,7,364,858, 7,358,048, 7,332,285, 7,320,865, 7,312,039, 7,244,831,7,198,894, 7,166,434, 7,097,980, 7,083,917, 7,014,994, 6,949,370,6,852,487, 6,797,470, 6,576,453, 6,534,293, 6,506,594, 6,312,892, and6,268,148 describe the use of the ligase detection reaction withdetection reaction (“LDR”) coupled with polymerase chain reaction(“PCR”) for nucleic acid detection.

Barany et al., U.S. Pat. Nos. 7,556,924 and 6,858,412, describe the useof padlock probes (also called “precircle probes” or “multi-inversionprobes”) with coupled ligase detection reaction (“LDR”) and polymerasechain reaction (“PCR”) for nucleic acid detection.

Barany et al., U.S. Pat. Nos. 7,807,431, 7,709,201, and 7,198, 814describe the use of combined endonuclease cleavage and ligationreactions for the detection of nucleic acid sequences.

Willis et al., U.S. Pat. Nos. 7,700,323 and 6,858,412, describe the useof precircle probes in multiplexed nucleic acid amplification, detectionand genotyping

Ronaghi et al., U.S. Pat. No. 7,622,281 describes amplificationtechniques for labeling and amplifying a nucleic acid using an adaptercomprising a unique primer and a barcode.

In addition to the various amplification techniques, numerous methods ofsequence determination are compatible with the processes and systems ofthe inventions. Preferably, such methods include “next generation”methods of sequencing. Exemplary methods for sequence determinationinclude, but are not limited to, hybridization-based methods, such asdisclosed in Drmanac, U.S. Pat. Nos. 6,864,052; 6,309,824; and6,401,267; and Drmanac et al, U.S. patent publication 2005/0191656,which are incorporated by reference, sequencing by synthesis methods,e.g., Nyren et al, U.S. Pat. Nos. 7,648,824, 7,459,311 and 6,210,891;Balasubramanian, U.S. Pat. Nos. 7,232,656 and 6,833,246; Quake, U.S.Pat. No. 6,911,345; Li et al, Proc. Natl. Acad. Sci., 100: 414-419(2003); pyrophosphate sequencing as described in Ronaghi et al., U.S.Pat. Nos. 7,648,824, 7,459,311, 6,828,100, and 6,210,891, andligation-based sequencing determination methods, e.g., Drmanac et al.,U.S. Pat. Appln No. 20100105052, and Church et al, U.S. Pat. Appln Nos.20070207482 and 20090018024.

Alternatively, nucleic acid regions of interest can be selected and/oridentified using hybridization techniques. Methods for conductingpolynucleotide hybridization assays for detection of have been welldeveloped in the art. Hybridization assay procedures and conditions willvary depending on the application and are selected in accordance withthe general binding methods known including those referred to in:Maniatis et al. Molecular Cloning: A Laboratory Manual (2^(nd) Ed. ColdSpring Harbor, N.Y., 1989); Berger and Kimmel Methods in Enzymology,Vol. 152, Guide to Molecular Cloning Techniques (Academic Press, Inc.,San Diego, Calif., 1987); Young and Davis, P.N.A.S, 80: 1194 (1983).Methods and apparatus for carrying out repeated and controlledhybridization reactions have been described in U.S. Pat. Nos. 5,871,928,5,874,219, 6,045,996 and 6,386,749, 6,391,623 each of which areincorporated herein by reference

The present invention also contemplates signal detection ofhybridization between ligands in certain preferred aspects. See U.S.Pat. Nos. 5,143,854, 5,578,832; 5,631,734; 5,834,758; 5,936,324;5,981,956; 6,025,601; 6,141,096; 6,185,030; 6,201,639; 6,218,803; and6,225,625, in U.S. Patent application 60/364,731 and in PCT ApplicationPCT/US99/06097 (published as WO99/47964), each of which also is herebyincorporated by reference in its entirety for all purposes.

Methods and apparatus for signal detection and processing of intensitydata are disclosed in, for example, U.S. Pat. Nos. 5,143,854, 5,547,839,5,578,832, 5,631,734, 5,800,992, 5,834,758; 5,856,092, 5,902,723,5,936,324, 5,981,956, 6,025,601, 6,090,555, 6,141,096, 6,185,030,6,201,639; 6,218,803; and 6,225,625, in U.S. Patent application60/364,731 and in PCT Application PCT/US99/06097 (published asWO99/47964), each of which also is hereby incorporated by reference inits entirety for all purposes.

Multiplexed PCR and array-based pull-outs are alternative options. Withrespect to detection platforms, the most preferred option ishigh-throughput DNA sequencing such as with Illumina, Complete Genomicsand Ion Torrent. Array and qPCR read-outs are also possibilities. Afterthe fetal genotypes have been determined, one compares those fetalgenotypes to the phased parental genotypes. By using the haplotypeinformation, one can identify alleles that would have been inheritedtogether, thus identifying which chromosome or portions of chromosomeshave been inherited. Once one has identified which chromosome orportions of chromosome have been inherited, one can then impute thefetal sequence. In the case where portions of chromosomes have beeninherited, the sequence information between those portions isindeterminate. The amount of indeterminate sequence information ishighly dependent upon the number of genotypes determined. Increasing thenumber of genotypes decreases the amount of indeterminate sequenceinformation as one can determine with more certainty where therecombination site occurred. After the imputation of the fetal sequence,one may determine which clinically or phenotypically significantvariants the fetus has inherited from each parent. It is important tonote that one does not actually have to determine the fetal variant ofclinical significance directly in the maternal sample. This can be doneby imputing the variant from knowing the inheritance of other variants.

The processes and systems of the present invention utilize sequenceinformation from heritable regions of the maternal and paternal genometo “phase” the fetal DNA obtained from a maternal source to obtainhaplotype information for the heritable region of DNA. The parentalgenotypes for the heritable regions are determined using sequencing, andthe linked alleles are identified through the sequencing process. As thefetal DNA may be available in the maternal sample as shorter regions(e.g., cell free DNA fragments), phasing of the fetal DNA may be morecost-effective than deep sequencing and assembly of the fetal genome.

Sequence information may be determined using methods that determine many(typically thousands to billions) of nucleic acid sequences in anintrinsically parallel manner, where many sequences are read outpreferably in parallel using a high throughput serial process. Suchmethods include but are not limited to pyrosequencing (for example, ascommercialized by 454 Life Sciences, Inc., Branford, Conn.); sequencingby ligation (for example, as commercialized in the SOLiD™ technology,Life Technology, Inc., Carlsbad, Calif.); sequencing by synthesis usingmodified nucleotides (such as commercialized in TruSeq™ and HiSeq™technology by Illumina, Inc., San Diego, Calif., HeliScope™ by HelicosBiosciences Corporation, Cambridge, Mass., and PacBio RS by PacificBiosciences of California, Inc., Menlo Park, Calif.), sequencing by iondetection technologies (Ion Torrent, Inc., South San Francisco, Calif.);sequencing of DNA nanoballs (Complete Genomics, Inc., Mountain View,Calif.); nanopore-based sequencing technologies (for example, asdeveloped by Oxford Nanopore Technologies, LTD, Oxford, UK), and likehighly parallelized sequencing methods.

In some aspects, the fetal haplotypes are inferred by haplotyperesolution or haplotype phasing techniques. These methods work byapplying the observation that certain haplotypes are common in certaingenomic regions. Therefore, given a set of possible haplotyperesolutions, these methods choose those that use fewer differenthaplotypes overall.

In specific aspects, combinatorial approaches (e.g., parsimony) are usedfor haplotype phasing. In brief, haplotypes for an individual areselected among competing possible haplotpes and the one that offers thesimplest explanation of the data derived from the fetal DNA is used toidentify the most likely haplotypes for a heritable region.

In other specific aspects, likelihood functions are used. For example,haplotype phasing can be determined based on models and assumptions suchas those that utilize genetic equilibrium (e.g., the Hardy-Weinbergprinciple). In the simplest case of a single locus with two alleles: thedominant allele is denoted A and the recessive a and their frequenciesare denoted by p and q; freq(A)=p; freq(a)=q; p+q=1. If the populationis in equilibrium, then we will have freq(AA)=p² for the AA homozygotesin the population, freq(aa)=q² for the aa homozygotes, and freq(Aa)=2pqfor the heterozygotes.

Other aspects employ retrospective models of population genetics, e.g.,the coalescent theory model. Each of these models can be combined withoptimization algorithms such as expectation-maximization algorithm (EM),Markov chain Monte Carlo (MCMC), or hidden Markov models (HMM).

An example is in the case of cystic fibrosis (CF) testing. Bysequencing, one would know that perhaps one or more of the parents are aCF carrier. The parents would like to know whether the fetus hasinherited one allele, in which case it may be a CF carrier, or whetherthe fetus has inherited two alleles, in which case it may be symptomaticfor CF. By genotyping informative loci close to the CF gene in thematernal sample, one may determine which chromosomes were inherited bythe fetus and thus which CF alleles the fetus inherited from eachparent, determining the CF status of the fetus.

Current approaches for full-scale genomic phasing require too muchsequencing to be cost-effective. The processes of the invention usingphasing based on fetal DNA fragments would greatly reduce the amount ofsequencing necessary to determine the fetal genome in utero.

Techniques for Phasing the Fetal Genome

There are many ways to phase a mammalian genome, including long-rangesequencing (>1000 bp) to identify overlapping haplotype information,sequencing or genotyping of predecessors or descendants to determinewhich alleles were inherited together, and imputation bypopulation-based haplotype information.

For the present invention, information from one or both parents makes itpossible to phase the fetal genome (for the vast majority of SNP calls)using a maternal sample. The processes of the invention rely on the factthat for most situations, the alleles inherited from the maternal and/orpaternal genome can be provided, and these can be used not only toidentify the value of likelihood of a specific chromosome beinginherited by the fetus, but also identification of recombination eventsand the genomic.

For example, as illustrated in FIG. 1, if at a particular position, afetal genotype call is AB (101), the paternal genotype is AA, and thematernal genotype is BB, the fetal A allele must have come from thefather, and the fetal B allele must have come from the mother. Suchalleles where fetal phase can be determined are considered informative.The cumulative data can be processed to determine a value of likelihoodof a particular chromosome being inherited by the fetus. The A allelefrom the father is associated with a certain paternally-inherited fetalchromosome 103 while the B allele is associated with a certainmaternally-inherited fetal chromosome 105. FIG. 2 provides examples ofinformative alleles based on maternal, paternal and fetal genotype thatmay be used in the processes of the invention.

FIG. 3 illustrates the utility of informative loci in determining theallelic make-up, and therefore phasing, of a fetal chromosome. Theability to test a limited number of allelic variants to infer all of theother alleles inherited by the fetus is a central concept of theinvention. Thus, by determining the inheritance of the allels shown inbold, the processes of the invention allow an imputation of the entireallelic makeup of the parentally-inherited chromosomes. Data on thealleles of a maternal phased chromosome 301 and a paternal phasedchromosome 303 are provided, and the linked haplotype data from thesechromosomes used to identify the phasing of the corresponding inheritedfetal chromosomes 305. In this particular illustration, the fetalchromosomes each have a recombination event resulting in individualinherited chromosomes having alleles inherited from both paternal andmaternal chromosomes.

The informative loci from the maternal and paternal genome allow bothidentification of the likely chromosomes inherited and theidentification of the recombination event. The resulting data can beused to determine a value of likelihood that the inherited fetalchromosomes comprise specific linked alleles in view of therecombination events. Using the maternal and paternal phased genomicinformation, the likely inherited paternally-derived chromosome 307 andthe maternally-derived chromosome 309 inherited by the fetus can becalculated using parental data.

FIG. 4 demonstrates the instance in which heterozygosity betweenmaternal and paternal alleles can be informative. For example, if bothparents have the genotype AB, and the fetus has the genotype BB, thenboth parents must have contributed the B genotype to the fetus.

In other implementations, such as that illustrated in FIG. 5, thephasing of the fetal DNA can be only partially determined based on theallelic data of a maternal phased chromosome 501 and a paternal phasedchromosome 503. This data can be used to identify the phasing of thecorresponding inherited fetal chromosomes 505. As in FIG. 3, the fetalchromosome has a recombination event in the DNA inherited from both thepaternal and the maternal genome. The linked allelic information in FIG.5, however, is ambiguous regarding the exact location of therecombination event due to heterozygosity at the maternal and paternalalleles at the site of recombination, so a value of likelihood for thefetal chromosomes can be determined on opposite sides of therecombination event but only as provided based on the availableinformative loci.

As the distinct position of the recombination event is unclear, a valueof probability can be calculated given different markers and the valueof likelihood that a recombination event may have occurred in a specificregion of the chromosome. Using the maternal and paternal phased genomicinformation, the paternally-inherited fetal chromosome 507 and thematernally-inherited fetal chromosome 509 can be calculated but moreinformation needs to be obtained in the recombination region todetermine the allelic composition of the region.

In a preferred aspect, the processes of the invention utilizes paternalgenomic information, maternal genomic information, andempirically-derived data from a maternal sample that comprises bothmaternal (the “major source”) and fetal (“the minor source”) DNA. Thecomputational process provides a removal of all paternal and maternalgenomic data which is the same across parental alleles, i.e., in whichall homozygous loci that are the same between the mother and father areremoved from the data set. Next, loci that are informative for thepaternal allele in the fetus (i.e., “minor source informative”) aredetermined, and alleles that are specific to the paternal source areidentified. This can be calculated using the empirically-derived datafrom the maternal sample, using counts determined from the nucleic acidspresent representative of each allele present in the maternal sample.One example of this is the use of a binomial equation such as: Bin(A+B,X), where A is the empirically determined level of a first allele, B isthe empirically determined level of a second allele, and X is a factorof the fetal contribution to the maternal sample. For example if thefetal contribution is approximately 10%, then X=0.05.

For the equation to have sufficient power, X>β, where β is the minimumlevel of fetal contribution in a sample. The value of β may depend uponthe number of informative loci used and the amount of parentalinformation available to be used in the processes of the invention.

From this information, the paternal contribution can be inferred formultiple minor source haplotypes that are associated with the fetalchromosome inherited from the father.

Once the paternal alleles are identified for these regions, the maternalallele can be imputed based on the empirically-determined ratios of thenucleic acids representing the different alleles present in the maternalsample. If, for instance, the mother and father are both heterozygousfor an allele, the maternally-inherited allele is the same as thepaternally-inherited allele, and the fetal contribution X=0.05, then theidentified nucleic acids representative of the allele in the maternalsample would be approximately 55/100 counts for that allele. If,however, maternally-inherited allele is the same as different from thepaternally-inherited allele, and the fetal contribution X=0.05, then theidentified nucleic acids representative of the allele in the maternalsample would be approximately 50/100 counts for that allele.

Empirical Determination of Fetal Contribution in a Maternal Sample

Determining which genetic loci are contributed to the fetus frompaternal sources may in certain aspects utilize information on the fetalcontribution in a maternal sample. The estimation of fetal DNAproportion in a maternal sample, provides information used to calculatestatistically significant differences in dosages for alleles ofinterest, and thus collectively for heritable genomic regions ofinterest.

In certain aspects, determination of fetal polymorphisms requirestargeted SNP and/or mutation analysis to identify the presence of fetalDNA in a maternal sample. In one preferred aspect, the percent fetalcell free DNA in a maternal sample can be quantified using multiplexedSNP detection based on knowledge of the maternal and/or paternalgenotype. The selected polymorphic nucleic acid regions from thematernal sample (e.g., plasma) are amplified. In a preferred aspect, theamplification is universal; and in a preferred embodiment, the selectedpolymorphic nucleic acid regions are amplified in one reaction in onevessel. Each allele of the selected polymorphic nucleic acid regions isdetermined and quantified. In a preferred aspect, high throughputsequencing is used for such determination and quantification.

Identification of informative loci is accomplished by observing a highfrequency of one allele (>80%) and a low frequency (<20% and >0.15%) ofthe other allele for a particular selected nucleic acid region. The useof multiple loci is particularly advantageous as it reduces the amountof variation in the measurement of the abundance of the alleles betweenloci. All or a subset of the loci that meet this requirement can used todetermine fetal contribution through statistical analysis. In oneaspect, fetal contribution is determined by summing the low frequencyalleles from two or more loci together, dividing by the sum of the lowand high frequency alleles and multiplying by two.

In one aspect, data from selected nucleic acid regions may be excludedif the data from the region appears to be an outlier due to experimentalerror or from idiopathic genetic bias within a particular sample. Inanother aspect, selected data from certain nucleic acid regions mayundergo statistical or mathematical adjustment such as normalization,standardization, clustering, or transformation prior to summation oraveraging. In another aspect, data from selected nucleic acid regionsmay undergo both normalization and data experimental error exclusionprior to summation or averaging.

In a preferred aspect, data from 12 or more nucleic acid regions or lociare used for the analysis. In another preferred aspect, data from 24 ormore nucleic acid regions or loci are used for the analysis. In anotherpreferred aspect, data from 48 or more loci are used for the analysis.In another aspect, one or more indices are used to identify the sample,the locus, the allele or the identification of the nucleic acid. Suchindices are as is described in co-pending applications U.S. Ser. Nos.13/205,490 and 13/205,570 hereby incorporated herein by reference intheir entirety.

In one preferred aspect, the percentage fetal contribution in a maternalsample is quantified using tandem SNP detection in the maternal andfetal alleles. Techniques for identifying tandem SNPs in DNA extractedfrom a maternal sample are disclosed in Mitchell et al, U.S. Pat. No.7,799,531 and U.S. Ser. Nos. 12/581,070, 12/581,083, 12/689,924, and12/850,588. These references describe the differentiation of fetal andmaternal loci through detection of at least one tandem single nucleotidepolymorphism (SNP) in a maternal sample that has a different haplotypebetween the fetal and maternal genome. Identification and quantificationof these haplotypes can be performed directly on the maternal sample andused to determine the fetal proportion of nucleic acids in the maternalsample.

Determination of Fetal DNA Content in a Maternal Sample Using EpigeneticAllelic Ratios

Certain genes have been identified as having epigenetic differencesbetween the fetus and the mother, and such genes are candidate loci forfetal DNA markers in a maternal sample. See, e.g., Chim, et al., PNASUSA, 102:14753-58 (2005). These loci, which are unmethylated in thefetus but are methylated in maternal blood cells, can be readilydetected in maternal plasma. The comparison of methylated andunmethylated amplification products from a maternal sample can be usedto quantify the percent fetal DNA contribution to the maternal sample bycalculating the epigenetic allelic ratio for one or more of suchsequences known to be differentially-methylated in fetal DNA as comparedto maternal DNA.

To determine methylation status of nucleic acids in a maternal sample,the nucleic acids of the sample are subjected to bisulfite conversion.Conventional processes for such bisulphite conversion include, but arenot limited to, use of commercially available kits such as theMethylamp™ DNA Modification Kit (Epigentek, Brooklyn, N.Y.). Allelicfrequencies and ratios can be directly calculated and exported from thedata to determine the percentage of fetal DNA in the maternal sample.

Human Reference Sequences

One of the challenges to interpretation of genome sequence data is theassembly and variant calling of sequence reads against the humanreference genome. Although de novo assembly of genome sequences from rawsequence reads represents an alternative approach, computationallimitations and the large amount of mapping information encoded inrelatively invariant genomic regions make this an unattractive optionpresently. The National Center for Biotechnology Information (NCBI)human reference genome (Pruitt K D et al., Nucleic Acids Res. 2012January; 40(Database issue):D130-5. Epub 2011 Nov. 24) is derived fromDNA samples from a small number of anonymous donors and thereforerepresents a small sampling of the broad array of human geneticvariation. For purposes of more diverse populations (or populations ofspecific descent) or more tailored genomes (individual genomes orcumulative reference of multiple genomes).

In some aspects of the invention, synthetic human reference sequencesthat are ethnically concordant with a pregnant subject and her familyare used for the analysis of genomes from a nuclear family. Suchreference sequences are described, e.g., in Dewey F E et al., PLoSGenet. 2011 September; 7(9):e1002280. Epub 2011 Sep. 15. The use of amajor allele reference sequence results in improved genotype accuracyfor variant loci. Recombination sites can be inferred to the lowestmedian resolution demonstrated to date (<1,000 base pairs).

Determination of the whole genome sequence of the mother and fetus, andpreferably the mother, father and fetus allows multigenic risk forinherited diseases and disorders, and may also be useful in optimizingpharmaceutical intervention based on metabolism or predicted response tovarious drugs. These ethnicity-specific, family-based approaches tointerpretation of genetic variation are emblematic of the nextgeneration of genetic risk assessment using whole-genome sequencing.

Computer Implementation of the Processes of the Invention

FIG. 6 is a block diagram illustrating an exemplary system environment60 in which the processes of the present invention may be implementedfor calculating chromosome or loci dosage and fetal DNA contribution.The system 60 includes a server 62 and a computer 66. The computer 66may be in communication with the server 62 through the same or differentnetwork 68.

According to the exemplary embodiment, the computer 66 executes asoftware component 64 that calculates fetal phased genomic informationbased on the provided data sets 74. In one embodiment, the computer 66may comprise a personal computer, but the computer 66 may comprise anytype of machine that includes at least one processor and memory.

The output of the software component 64 comprises a report 72 with avalue of likelihood of inheritance of one or more heritable genomicregions. The report 72 may be paper that is printed out, or electronic,which may be displayed on a monitor and/or communicated electronicallyto users via e-mail, FTP, text messaging, posted on a server, and thelike.

Although the process of the invention is shown as being implemented assoftware 64, it can also be implemented as a combination of hardware andsoftware. In addition, the software 64 may be implemented as multiplecomponents operating on the same or different computers.

Both the server 62 and the computer 66 may include hardware componentsof typical computing devices (not shown), including a processor, inputdevices (e.g., keyboard, pointing device, microphone for voice commands,buttons, touchscreen, etc.), and output devices (e.g., a display device,speakers, and the like). The server 62 and computer 66 may includecomputer-readable media, e.g., memory and storage devices (e.g., flashmemory, hard drive, optical disk drive, magnetic disk drive, and thelike) containing computer instructions that implement the functionalitydisclosed when executed by the processor. The server 62 and the computer66 may further include wired or wireless network communicationinterfaces for communication.

While this invention is satisfied by aspects in many different forms, asdescribed in detail in connection with preferred aspects of theinvention, it is understood that the present disclosure is to beconsidered as exemplary of the principles of the invention and is notintended to limit the invention to the specific aspects illustrated anddescribed herein. Numerous variations may be made by persons skilled inthe art without departure from the spirit of the invention. The scope ofthe invention will be measured by the appended claims and theirequivalents. The abstract and the title are not to be construed aslimiting the scope of the present invention, as their purpose is toenable the appropriate authorities, as well as the general public, toquickly determine the general nature of the invention. In the claimsthat follow, unless the term “means” is used, none of the features orelements recited therein should be construed as means-plus-functionlimitations pursuant to 35 U.S.C. § 112, ¶16.

The invention claimed is:
 1. A process for determining the phasedcomposition in a fetal heritable genomic region from a maternal samplecomprising maternal DNA and fetal DNA, the process comprising the stepsof: isolating cell-free nucleic acids from the maternal samplecomprising the maternal DNA and the fetal DNA, wherein the cell-freenucleic acids comprise selected nucleic acid regions; interrogating theselected nucleic acid regions in the fetal heritable genomic regionusing oligonucleotides to amplify the selected nucleic acid regions, theoligonucleotides comprising universal amplification sequences; applyingthe amplified selected nucleic acid regions to an array-based pull-outdetection system to identify informative loci corresponding to aheritable genomic region of interest; providing, to a computerprocessor, phased sequence information from at least one correspondingparental heritable genomic region; identifying, by the computerprocessor, five or more informative loci in the fetal DNA correspondingto a heritable genomic region of interest from the phased sequenceinformation of the at least one corresponding parental heritable genomicregion; calculating, by the computer processor, a paternal contributionof the heritable genomic region of interest using the phased sequenceinformation of the five or more informative loci; calculating, by thecomputer processor, the maternal contribution of the heritable genomicregion of interest by comparing the paternal contribution of theheritable genomic region of interest to the selected nucleic acidregions in the fetal heritable genomic region; and generating, by thecomputer processor, a prediction of a likely phased composition of theheritable genomic region of interest in the fetal DNA using the maternaland paternal contributions of the heritable genomic region of interest.2. The process of claim 1, wherein the maternal sample is a cell freematernal sample.
 3. The process of claim 2, wherein the cell freematernal sample is maternal plasma or serum.
 4. The process of claim 1,wherein the maternal sample comprises fetal cells.
 5. The process ofclaim 1, wherein a fetal genetic variation within the heritable genomicregion is imputed from a subset of parental informative loci.
 6. Theprocess of claim 1, wherein the phased sequence information of theheritable genomic region is determined by sequencing of the parentalgenome.
 7. The process of claim 1, wherein the phased sequenceinformation of the corresponding parental heritable genomic region isdetermined by pedigree analysis.
 8. The process of claim 1, wherein thephased composition in the fetal heritable genomic region comprisessequence information on at least twenty informative loci in theheritable genomic region.
 9. The process of claim 1, wherein the phasedcomposition in the fetal heritable genomic region comprises sequenceinformation on at least fifty informative loci in the heritable genomicregion.
 10. The process of claim 1, wherein the phased composition inthe fetal heritable genomic region comprises sequence information on atleast one hundred informative loci in the heritable genomic region. 11.The process of claim 1, wherein the heritable genomic region comprises asub-chromosomal unit.
 12. The process of claim 1, wherein the heritablegenomic region comprises an entire chromosome.
 13. The process of claim1, wherein the heritable genomic region comprises the entire genome.